Work machines such as wheel loaders and the like include drivetrain to drive traction devices such as wheels, tracks and the like to propel the work machine over a work surface. In one typical drivetrain arrangement, a power source, such as an internal combustion engine, is operatively connected to an automatic transmission by a torque converter. The transmission is in turn operatively connected to an axle that turns the traction devices to propel the machine over a work surface. The automatic transmission is connected to the power source by a torque converter that replaces the manual clutch of a manual transmission. The torque converter is a fluid coupling that allows the power source to operate at low speeds, such as when the power source is idling, without being fluidly coupled to the transmission. At higher power source speeds that create greater fluid pressure within the torque converter, the pressurized fluid drives the transmission and transfers the rotating power from the power source to the rotating driven load presented by the transmission to drive the transmission and the traction devices to propel the machine. The torque converter may include a lock-up clutch that can be locked so a power source output shaft and a transmission input shaft rotate at the same speed, and unlocked to allow the shafts to rotate at different speeds. An example of a torque converter and lock-up clutch arrangement is provided in U.S. Pat. No. 4,961,484, issued to Kato et al. on Oct. 9, 1990, entitled “Brake Device for a Vehicle.”
Present machines further include brake force devices applying brake forces to the machine on components such as axle on which the traction devices are mounted. The brake force devices apply brake force to the components in response to an operator of the machine displacing a brake input device within an operator station of the machine. The brake force reduces the ground speed of the machine over the work surface, eventually to the point where the transmission will downshift to a lower gear. In these arrangements, the lock-up clutch is unlocked if necessary shortly after displacement of the brake input device is detected, and the drivetrain provides minimal retarding force on the machine during braking due to slippage in the torque converter. As a result, the brake force device provides the majority of the retarding of the machine so that the brake force devices and the engaged components of the machine experience the wear and tear and heat generation associated with braking the machine.